1. Field of the Invention
This invention relates to television systems and, in particular, to such systems for displaying on-screen display (OSD) information from an external source.
2. Description of Related Art
Television systems receive signals from a variety of sources for displaying the signals on television monitors. Conventional television signals are analog and are typically sent directly to the television receiver via cable, satellite, or terrestrial transmissions using analog standards such as NTSC, PAL, and SECAM. However, as the number of different types of signal sources increases, external devices coupled to the television are needed to receive the signal and transmit the signal to television receiver. These external devices can include set-top boxes (STBs), video cassette recorders (VCRs), satellite dishes, and cable boxes for receiving signals from transmission methods such as direct satellite service (DSS), microwave broadcast, cellular television (xe2x80x9cwireless cablexe2x80x9d), and television delivered via digital telephone phone lines.
Such transmission methods allow consumers to receive a variety of entertainment and information services on their television sets. For example, a consumer may receive a basic selection of programs, or special premium channel programs may be chosen for an additional charge. Information services such as stock prices, teletext for the hearing impaired and others, or weather forecasts may also be received and displayed on the television monitor.
For the television monitor to be able to display these signals, the STB (which will be used throughout the description to represent any external device for receiving and transmitting signals to the television) demodulates and decodes the signal to an acceptable analog format, such as NTSC. Typically, the STB outputs a composite analog signal, which also contains on-screen display (OSD) information from the device. The OSD information is displayed on the television monitor for operation of the STB. Using information from the OSD, the viewer can tune to specific channels from the STB, adjust parameters such as picture intensity, contrast, or color tone, or control a peripheral device such as a VCR.
The OSD information is typically generated by a CPU within the STB. When the input from a TV monitor is switched to the external output of the STB, the OSD of the STB is available and visible on the TV display monitor because all displays have the same aspect ratio (e.g., 4:3) and scanning format (e.g., NTSC) so that the OSD signal is compatible with the display on the TV monitor.
More recently, signals are also being transmitted digitally, such as in standard definition (SD) by Digital Satellite System (DSS). Digital signals are encoded according to an MPEG (Moving Picture Expert Group) standard, transmitted, and received by an appropriate STB coupled to a television monitor. The STB device, such as a DSS receiver, digital cable box, or DVD recorder, contains a standard, main-level MPEG decoder for decoding the SD digital signal into SD analog signal, e.g., NTSC. The SD analog signal is superimposed with the OSD signal generated by the CPU within the STB. The resulting analog signal is transmitted from the STB output to the input of a television monitor, where the OSD information is extracted from the signal for display on the television monitor. Consequently, operation of the STB, such as to navigate through channels in the STB, is possible because the SD digital signal has been decoded and merged with the OSD information in an analog signal format, which is compatible with the television monitor (i.e., 4:3 aspect ratio, NTSC scanning standard, etc.).
However, the MPEG decoders in current STBs are unable to decode high definition (HD) digital signals. Thus, a STB will typically demodulate and pass the HD signal in digital form to the input of a high definition television (HDTV), typically through a high speed digital interface, such as the IEEE 1394 interface. A high-level MPEG-2 decoder inside the HDTV will then decode the HD digital signal for display on the television monitor, which displays a 16:9 aspect ratio picture instead of the conventional 4:3 aspect ratio standard definition picture. However, the OSD information for the STB generated by the STB CPU is still in analog form. Furthermore, the STB does not know the on-screen display (OSD) capability, the aspect ratio, or native display scanning format of the television monitor. Thus, the analog OSD information cannot be included with the HD signal in the digital transport stream to the monitor. As a result, no OSD information is available to the HDTV, and operation of the STB is not possible.
One possible solution for providing OSD information to HDTVs is to include a high-level MPEG-2 decoder in the STB. The HD digital signals being received by the STB can then be decoded by the MPEG-2 decoder and superimposed with the internally generated OSD information. The resulting signal, with OSD information, can then be sent to the HDTV. However, one significant problem is that this signal has a very high transmission bandwidth, which cannot be transmitted practically with current interfaces, such as the IEEE 1394. Therefore, before transmission, the decoded signal with OSD information can be encoded and compressed with a high-level MPEG-2 encoder in the STB to reduce the transmission bandwidth. This approach is very cost prohibitive due to the need for a high-level MPEG-2 decoder and encoder in the STB, particularly since HD digital broadcasts are in their infancy and few programs are being transmitted in the HD digital format. Furthermore, televisions capable of displaying high definition digital pictures currently constitute only a small percentage of the televisions in use today. Consequently, STB manufacturers are reluctant to build high-priced STBs with high-level decoding capabilities because only a small percentage of televisions would utilize this feature. Thus, current HDTVs have high-level MPEG-2 decoders built into the television for decoding the high definition digital signals received from the STBs in order to display the high definition images.
However, as mentioned above, the high definition signal coming into the television is digital, while the OSD information for the STB is analog. As a result, the OSD information for the STB is incompatible with the HDTV, thereby rendering the STB on-screen display information inoperable with the HDTV display.
Accordingly, it is desirable for a high definition television to be able to display and utilize analog on-screen information from a set-top box without greatly increasing the cost to the television system.
In accordance with an aspect of the invention, a method and system are provided which allows the on-screen display (OSD) information from a set-top box (STB) or other external display device to be displayed on a high definition television (HDTV) by transmitting separate signals for the digital high definition image and for the analog OSD information for the STB to the HDTV and by processing the OSD information in the STB and the high definition signal in the HDTV.
The high definition digital signal is demodulated and demultiplexed in the STB and then transmitted out of the STB via a high speed digital interface, such as IEEE1394. Also, OSD information for the STB is generated within the STB. The OSD information is decoded and converted to an analog signal and transmitted out of the STB via an analog interface. The HD digital signal and the analog OSD signal are sent to a digital input and an analog input, respectively, of the HDTV. Within the HDTV, a high-level MPEG-2 decoder decodes the HD digital signal for display on the HDTV monitor. However, when the OSD information for the STB is needed, the HDTV switches the display input to the analog signal carrying the STB OSD information. The OSD information is displayed along with or instead of the HD video display. When the OSD information is displayed, the user can access the STB via the on-screen information.
In other embodiments, the OSD information for the STB is transmitted out of the STB along the digital transport stream, along with the HD digital data, via a high speed digital interface, such as IEEE1394. The HDTV demultiplexes and decodes the digital transport stream to extract the OSD information for display on the HDTV monitor. Thus, functions in the STB can be accessed from the displayed OSD information.
The present invention will be more fully understood upon consideration of the detailed description below, taken together with the accompanying drawings.